The Australian government has confirmed the identification of two “acoustic events” that match the frequency signals of airplane black boxes and flight recorders, but stressed that such an identification does not definitively mean they have found missing Malaysia Airlines Flight 370’s black boxes.

After the single biggest breakthrough in the search for the missing flight yesterday–a Chinese vessel recording a 37.5kHz frequency matching airplane emergency gear signals–Australian search vessels confirmed that they had encountered two similar “acoustic events” in the area similar to that of the first frequency ping. According to the Sydney Morning Herald, the head of the search for Flight 370, Air Chief Marshal Angus Houston, told the media that the new signals “provide some promise,” but emphasized the need for caution before determining whether the lead will develop into a significant finding.

Flight 370’s black boxes are set to send out frequency signals until their batteries run out, and batteries are expected to last around 30 days. This means that the black boxes could stop sending signals out at any minute, or might have already ceased doing so.

Houston also noted that the search area was being slightly modified after some new analysis of radar evidence. The new location, further south than the original search area, puts the location where Chinese vessel Haixun 01 heard radar signals closer to the center of the search area. “The search area doesn’t change so it’s not a big change,” Chief Marshal Houston said, according to the Wall Street Journal. “…but the area of highest probability we think is now probably in the southern part of the area pretty close to where Haixun 01 is operating.”

Haixun 01 also detected a second signal within 1.4 miles of the first, though reports note that the presence of other vessels in the area could have affected the ships ability to pick up signals. Houston reported that both China and Australia were moving their ships into the area where the pings were coming from, but warned that, given the depth of the ocean in that area, any immediate finds were unlikely.

CNN reports that relatives of the passengers aboard Flight 370 are treating the new leads with healthy skepticism, after being told of several investigative leads that fizzled out. “We want something solid before commenting right now,” one relative told the news outlet, while another, a Chinese relative in Kuala Lumpur for the investigation, denounced the Malaysian government. “We will never forgive for covering the truth from us and the criminal who delayed the rescue mission,” said Jiang Hui, a relative designated representative for a larger group outraged with the length of the search and the lack of information provided to them.